Photoluminescence quenching of tris-(8-hydroxyquinoline) aluminum thin films at interfaces with metal oxide films of different conductivities

We report a comprehensive study of photoluminescence (PL) quenching of tris-(8-hydroxyquinoline) aluminum (Alq(3)) at interfaces with thin films of tin oxide (SnO(2)) using both steady-state and time-resolved measurements. Quenching of excitons generated in the Alq(3) layer increased with increased conductivity of the SnO(2) films, which we relate with the presence of nonradiative energy transfer from excitons in Alq(3) to transitions in SnO(2). In addition, due to the semitransparency of SnO(2), the effects of optical interference on the steady-state PL quenching of Alq(3) are determined. We demonstrate that without accounting for the interference effects in the excitation, the extracted exciton diffusion length (L(d)) in Alq(3) is in the range of 10-20 nm. However, when using a numerical model to account for the optical interference effects, we find that L(d) is in the range of 5-9 nm, which agrees with L(d) extracted from time-resolved measurements (4-6 nm). We conclude that time-resolved measurements are least affected by optical interference, yielding the most accurate measurement of L(d).